Plethron (πλέθρον) is a measurement used in Ancient times, equal to 100 Greek feet (pous/ποῦς). It was roughly the width of a typical athletic running-track, and was used as the standard width and length of a Wrestling square, since wrestling competitions were held on the racing track in early times.
A plethron is given as the size of the wrestling area by Libanius in Orationes Chapter 10.
Although the standard measure for a plethron may have varied from polis to polis, it normally corresponded to the length of around 30 meters (100 ft). A square plethron is consequently a square of around 30 by 30 meters, i. e. something like 900 square meters.
The plethron continued to be used in the Byzantine Empire and was defined as 100 feet or 40 paces (bema/βῆμα); one square plethron was a stremma.[1]